Metering device for a nozzle of an injection molding apparatus

ABSTRACT

An injection molding apparatus includes an injection piston that is slidable within a nozzle having a movable valve gate pin. The injection piston is movable from a retracted position to an extended position in order to force melt towards a mold cavity. A valve is located at a forward end of the piston to selectively block communication between a recess, which is provided in an outer wall of the piston adjacent the valve, and a melt chamber of the nozzle. Movement of the injection piston from the retracted position to the extended position causes the valve to close so that the predetermined volume of melt located below the valve is forced into the mold cavity, when the valve gate pin opens the mold gate.

FIELD OF THE INVENTION

[0001] The present invention relates generally to an injection moldingapparatus, and in particular to a metering device for a not runnernozzle, which injects a predetermined quantity of melt into a moldcavity.

BACKGROUND OF THE INVENTION

[0002] In an injection molding apparatus, a manifold receives apressurized melt stream from a machine nozzle. The manifold distributesthe melt stream to a plurality of nozzles and the melt is forced throughthe nozzles and into a plurality of mold cavities. The melt is thencooled in the mold cavities and the molded parts are released so thatanother cycle can begin.

[0003] The amount of melt transferred to each nozzle can vary due toeffects such as shear induced flow imbalance in the manifold, forexample. In order to compensate for such effects and ensure that asufficient amount of melt is delivered to each mold cavity, the pressureapplied to the melt stream by the machine nozzle must be very high. Forapplications such as injection molding of thin walled vessels andmicro-molding, even higher nozzle pressures are required in order toproduce quality molded products. As a result, the machine nozzle must bevery large in order to generate sufficient pressure to properlydistribute the melt to the mold cavities. In many cases, however,increasing the size of the machine nozzle is not a practical solution.Alternative solutions for increasing the pressure generated in eachindividual nozzle are therefore desirable.

[0004] Precise measurement of the volume of melt transferred in eachshot for thin walled molded parts and micro-molded parts is also veryimportant. This presents a unique challenge particularly when dealingwith micro molded parts, which typically weigh a fraction of a gram.Several prior art devices have been developed to control the volume ofmelt that is injected into a mold cavity. These devices have typicallybeen employed when injecting more than one material into a single moldcavity and tend to be complex and costly to manufacture.

[0005] U.S. Pat. No. 5,112,212 to Akselrud et al. discloses a shootingpot, which is used as a metering device, for use in a co-injectionmolding apparatus. The shooting pot is located remote from the hotrunner nozzle and is used to control the volume of one of the two moltenmaterials injected into the cavity. The shooting pot includes a pistonthat is axially movable within a cylinder to force molten material fromthe cylinder into a nozzle, which leads to a mold cavity. The cylinderincludes an inlet that delivers melt from a melt source to a reservoir,which is located in a lower end of the piston. The piston is rotatableto move the reservoir out of communication with the inlet to seal it offso that when the piston is lowered, a known volume of melt is forcedinto the mold cavity.

[0006] U.S. Pat. No. 4,863,369 to Schad et al. discloses an injectionmolding apparatus that uses a shooting pot to deliver a preciselymeasured quantity of melt to a mold cavity. A valve is located in aconduit between a melt source and each nozzle. Once the shooting pot andnozzle are filled with melt, the valve is closed and the mold gate isopened. A piston of the shooting pot advances until it bottoms out in acylinder to deliver a precise quantity of melt to a mold cavity.

[0007] A disadvantage of shooting pots that are remotely located fromthe nozzle and the mold cavity is that the known or measured volume ofmelt may vary from one molding cycle to the next. This occurs becausethere is a large volume of melt that is located between the shooting potand the mold cavity i.e. the melt in the nozzle, the melt in themanifold channel and the melt in the shooting pot. This large volume ofmelt introduces several variables. Minor deviations in temperature orpressure, for example, may result in significant variations of the knownvolume. The sizable distance between the shooting pot and the moldcavity further causes the melt to have a long residence time outside ofthe nozzle between the injection of one article to the next. Thisresults in molded parts that are not of the highest quality because thetemperature of the melt coming from the shooting pot may be either underheated or over heated.

[0008] It is therefore an object of the present invention to provide ametering device for a nozzle of an injection molding apparatus, whichobviates or mitigates at least one of the above disadvantages.

SUMMARY OF THE INVENTION

[0009] According to one aspect of the present invention there isprovided an injection molding apparatus comprising:

[0010] a manifold having a manifold channel for receiving a melt streamof moldable material under pressure, the manifold channel having anoutlet for delivering the melt stream to a nozzle channel of a nozzle;

[0011] a mold cavity receiving the melt stream from the nozzle, thenozzle channel communicating with the mold cavity through a mold gate;

[0012] a gating mechanism for selectively closing the mold gate;

[0013] a piston extending through the nozzle channel of the nozzle andbeing slidable therethrough, an outer wall of the piston abutting aninner wall of the nozzle channel, the piston being movable from aretracted position to an extended position to force melt towards themold cavity;

[0014] a valve located at a forward end of the piston, the valve beingselectively movable to block communication between a recess, which isprovided in the outer wall of the piston adjacent the valve, and a meltchamber of the nozzle channel, the valve being open to allow melt toflow from the manifold channel into the recess and into the melt chamberof the nozzle channel when the piston is in the retracted position;

[0015] wherein movement of the piston towards the extended positionforces melt located in the melt chamber of the nozzle channel to flowinto the mold cavity.

[0016] According to another aspect of the present invention there isprovided a method for forcing melt into a mold cavity of an injectionmolding apparatus, the method comprising:

[0017] closing a mold gate of the mold cavity to block a melt streamfrom flowing from a nozzle channel of a nozzle into the mold cavity;

[0018] maintaining a piston located in the nozzle channel in a retractedposition, in which a valve located at a forward end of the piston isopen to enable the melt stream to flow from a manifold channel of amanifold, through a recess provided adjacent the forward end of thepiston into a melt chamber of the nozzle channel, to fill the nozzlechannel with melt;

[0019] closing the valve to block flow of the melt stream between therecess and the melt chamber of the nozzle channel;

[0020] opening the mold gate; and

[0021] moving the piston towards an extended position to force the meltlocated in the melt chamber of the nozzle channel into the mold cavity.

[0022] According to another aspect of the present invention there isprovided a piston for a nozzle of an injection molding apparatuscomprises:

[0023] a valve located on a forward end of the piston, the valve beingselectively closable to block communication between a recess, which isprovided in the outer wall of the piston adjacent the valve, and a meltchamber of a nozzle channel; and

[0024] wherein the valve is open to allow melt to flow from the recesspast the valve when the piston is in a retracted position and the valveis closed when the piston is moved toward an extended position in orderto force melt into a mold cavity.

[0025] According to yet another aspect of the present invention there isprovided an injection molding apparatus comprising:

[0026] a manifold having a manifold channel for receiving a melt streamof moldable material under pressure, the manifold channel having anoutlet for delivering the melt stream to a nozzle channel of a nozzle;

[0027] a mold cavity receiving the melt stream from the nozzle channel,the nozzle channel communicating with the mold cavity through a moldgate;

[0028] a gating mechanism for selectively closing the mold gate;

[0029] a melt chamber located in the nozzle channel adjacent the moldgate, the melt chamber having a predetermined volume;

[0030] a valve located between the outlet of the manifold channel andthe melt chamber, the valve being selectively movable to control meltflow from the manifold channel into the melt chamber; and

[0031] wherein the predetermined volume of melt is injected into themold cavity in a single shot.

[0032] According to still another embodiment of the present inventionthere is provided a method of injecting a predetermined volume of amolten material into a mold cavity comprising:

[0033] a) injecting molten material through a hot runner manifold into avalve gated hot runner nozzle including a movable valve pin, where thevalve pin is in the closed position engaging a mold gate;

[0034] b) opening the mold gate;

[0035] c) injecting the molten material into a mold cavity through themold gate by moving an injection piston located at least partially inthe nozzle to transfer the predetermined volume of molten material fromthe hot runner nozzle into the mold cavity.

[0036] d) closing the communication between the hot runner nozzle andthe mold cavity by moving the valve pin into engagement with the moldgate.

[0037] According to another embodiment of the present invention there isprovided a method of injecting a predetermined volume of a moltenmaterial into a mold cavity comprising:

[0038] a) injecting molten material through a hot runner manifold into avalve gated hot runner nozzle including a movable valve pin, where thevalve pin is in the closed position engaging a mold gate;

[0039] b) blocking communication between the hot runner manifold and thehot runner nozzle;

[0040] c) opening the mold gate;

[0041] d) moving an injection piston located at least partially in thenozzle toward the mold gate to transfer the predetermined volume ofmolten material from the hot runner nozzle into the mold cavity;

[0042] e) closing the communication between the nozzle and the moldcavity by moving the valve pin into engagement with the mold gate.

[0043] The present invention provides an advantage in that a meteredquantity of melt is delivered consistently to a mold cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Embodiments of the present invention will now be described morefully with reference to the accompanying drawings.

[0045]FIG. 1 is a side sectional view of an injection molding apparatusof the present invention.

[0046]FIG. 2 is a side sectional view of a valve of a piston of FIG. 1.

[0047]FIG. 3 is a view on 3-3 of FIG. 2.

[0048]FIG. 4 is a view on 4-4 of FIG. 3.

[0049] FIGS. 5 to 9 are schematic side views of a portion of FIG. 1 atdifferent stages of the injection cycle.

[0050]FIG. 10 is a schematic side sectional view of another embodimentof an injection molding apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0051] Referring to FIG. 1, portions of an injection molding apparatusare generally shown at 10. The injection molding apparatus 10 comprisesa manifold 12 having a manifold melt channel 14 for receiving a meltstream of moldable material under pressure from a manifold bushing 16.The manifold bushing 16 is in communication with a machine nozzle (notshown). Bores 20 extend through the manifold 12 at distal ends of themanifold melt channel 14. The bores 20 are in communication with themelt channel 14 and extend generally perpendicular thereto.

[0052] Hot runner nozzles 18 are coupled to a lower surface of themanifold 12. A nozzle channel 22 of each nozzle 18 is aligned with arespective bore 20 to receive the melt stream of moldable material fromthe manifold 12. A mold gate 24 is located adjacent the tip of eachnozzle 18. The mold gates 24 are openable to allow delivery of the meltstream to respective mold cavities 26. Any number of nozzles 18 can beused to feed either a single or a plurality of mold cavities 26. Themold cavities 26 may be of the same size and shape or they may differ.Manifold heaters (not shown) and nozzle heaters 32 maintain the meltstream at a desired temperature and cooling channels (not shown)facilitate cooling of the mold cavities 26.

[0053] A metering device in the form of a hot runner injection piston 40is slidable through the bore 20 of the manifold 12 and the nozzle 18. Avalve pin 28 extends through a central bore 42 of the injection piston40 and is slidable therethrough to open and close the mold gate 24. Theinjection piston 40 and the valve pin 28 are driven independently andmove relative to one another. The valve pin 28 is pneumatically drivenby a valve piston 30 that is slidable in a cylinder 34. The injectionpiston 40 is pneumatically driven by a second piston 44 that is slidablein a second cylinder 46. The injection piston 40 and valve pin 28 arenot limited to being driven pneumatically, they may be also drivenhydraulically or by any other suitable means, including electrical andelectromagnetic motors. In addition, the valve pin 28 may be replaced byanother type of gating mechanism.

[0054] The injection piston 40 further comprises a piston body 50 thatextends outwardly from the second piston 44. The piston body 50 iscoupled to the second piston 44 by fasteners (not shown). Alternatively,the piston body 50 may be integral with the piston 44. The piston body50 includes an outer surface 51, which blocks the communication betweenthe manifold channel 14 and the nozzle channel 22 during movement of thepiston body 50 towards the mold cavity 26. An annular recess 48 isprovided in the outer surface 51 of the piston body 50. It will beappreciated that the annular recess 48 need not extend around the entirecircumference of the outer surface 51. A valve, generally indicated at52, is located at a forward end of the piston body 50 adjacent therecess 48. The valve 52 is openable to enable communication between therecess 48 and a melt chamber 54 of the nozzle channel 22. The meltchamber 54 of the nozzle channel 22 is located between the mold gate 24and the valve 52. When the injection piston 40 is in the retractedposition and the valve pin 28 is in the closed position, the volume ofthe melt in the melt chamber 54 of the nozzle 18 is known. The knownvolume of melt in the melt chamber 54 corresponds to the volume of meltto be injected into each mold cavity 26. The close proximity of theknown volume of melt to be injected and the mold cavity 26 reduces theamount of variability experienced by prior art devices.

[0055] Referring to FIGS. 2-4, the valve 52 is better illustrated. Thevalve comprises a flange 56 that extends outwardly from a lower end ofthe piston body 50. As shown in FIG. 3, the flange 56 includes a seriesof cutouts 58 that are spaced around the circumference thereof. A disc66 is axially movable relative to the flange 56. The disc 66 includes asecond series of cutouts 72 that are spaced around the circumferencethereof. The disc 66 is oriented so that the second series of cutouts 72is angularly offset from the series of cutouts 58 of the flange 56. Thedisc 66 and the flange 56 having the same outer diameter. Thisarrangement ensures that when the disc 66 abuts the flange 56, no meltcan flow past the valve 52 in either direction so that the desiredamount of melt, which is located in the melt chamber 54, is injectedinto the mold cavity 26.

[0056] The disc 66 further includes a stem 68 that extends outwardlytherefrom and an enlarged head 70 that is mounted on the end of the stem68. A central cavity 60 is provided in the lower end of the piston body50 to receive the enlarged head 70 and limit the distance of travelthereof. The enlarged head 70 abuts a shoulder 62 of the central cavity60 when the valve 52 is in the fully open position. The stem 68 isaxially movable through a square-shaped bore 64 to reciprocate the disc66 into and out of engagement with the flange 56. The square shape isused to prevent rotation of the disc 66 with respect to the flange 56.It will be appreciated that the stem 68 may be any shape orconfiguration that prevents rotation of the disc 66, for example, thestem 68 may be circular with a groove for receiving a dowel. The disc 66is movable together with and independent of the piston body 50 as aresult of the force exerted thereon by the melt in the nozzle channel.Retraction of the injection piston 40 causes the valve 52 to open bycreating a gap 80 between the flange 56 and the disc 66, and extensionof the injection piston 40 causes the valve 52 to close by eliminatingthe gap 80. Other arrangements may be used to provide a valve thatperforms the same function.

[0057] In operation, the pressurized melt stream flows through themanifold bushing 16 to the manifold channel 14 of the manifold 12.Referring to FIG. 5, the cycle begins with the mold gate 24 in theclosed position, in which the valve pin 28 engages the mold gate 24, andthe injection piston 40 in the retracted position. In the retractedposition, the recess 48 is aligned with the manifold channel 14 toreceive melt therefrom. The melt flows from the manifold 12 into therecess 48, which forces the valve 52 into the fully open position toallow melt to fill the nozzle channel 22. Once the nozzle 18 is full ofmelt, the injection piston 40 is moved toward the extended position asindicated by arrow 82 in FIG. 6. The forward movement of the injectionpiston 40 causes the disc 66 to be forced toward the flange 56 to closethe valve 52. At the same time, the outer surface 51 of the piston body50 shuts off communication between the manifold channel 14 and thenozzle channel 22. In this position, no additional melt can enter themelt chamber 54. Referring to FIG. 7, once the melt chamber 54 has beenisolated from the rest of the nozzle channel 22, the mold gate 24 isopened by retracting the valve pin 28, as indicated by arrow 84. Theforward stroke of the injection piston 40, indicated by arrow 86, thenforces the melt located in the melt chamber 54 of the nozzle channel 22into the mold cavity 26, as shown in FIG. 8. The mold gate 24 is thenclosed by extending the valve pin 28, as indicated by arrow 88 in FIG.9, and the injection piston 40 returns to the retracted position, asindicated by arrow 90. This returns the injection piston 40 and valvepin 28 to the positions of FIG. 5 so that the cycle can be repeated. Aswill be appreciated, this arrangement ensures that the volume of meltinjected into the mold cavity 26 is equal for each mold cavity 26 and isconstant for every cycle.

[0058] Referring to FIG. 10, another embodiment of an injection moldingapparatus 110 is shown. The numerals used previously in describing FIG.1 will be used again after raising the numerals by 100 where the partsto be described correspond to parts already described. The injectionmolding apparatus 110 is similar to the injection molding apparatus ofFIG. 1 with the addition of pressure sensors 200, 202 and 204, which areprovided in the mold cavity 126, the nozzle channel 122 and the manifold114, respectively. The pressure sensors 200, 202 and 204 sendinformation to the hot runner and mold controller 206 for use incontrolling the timing and sequence of movements of the injection piston140 and the valve pin 128. It will be appreciated that it is notnecessary to use all three pressure sensors 200, 202, 204. If desired,only one or two of the pressure sensors 200, 202, 204 may be used.

[0059] Temperature sensors 208 and 210 are provided to measure thetemperature of melt in the mold cavity 126 and in the nozzle 118,respectively. An additional sensor (not shown) may be provided in themanifold 112. Like the pressure sensors 200, 202, 204, the temperaturesensors 208, 210 also send information to the controller 206 for use incontrolling the timing and sequence of movements of the injection piston140 and the valve pin 128. The controller 206 communicates with a motiondrive 216 that, in turn, communicates with position sensors 212 and 214.The position sensors 212, 214 are used to control the position andmovement of the injection piston 140 and the valve pin 128,respectively. The sensors may be of any known type, such as, forexample, optical or inductive sensors. In some cases, only the positionsensors 212 and 214 may be used for the purpose of simplifying theinjection molding apparatus 110.

[0060] This arrangement is particularly useful in an injection moldingapparatus 110 in which all of the cavities have the same size. Thesensors 200, 202, 204 may be used to ensure that the pressure isgenerally equal in each of the mold cavities 126 and is generally equalbetween different batches of molded parts. The sensors 200, 202, 204 arealso useful in the case of a family mold, in which the pressure in eachmold cavity 126 is different and corresponds to a predetermined value.

[0061] Because a manifold typically supports more than one nozzle, itwill be appreciated by a person skilled in the art that the movement ofthe individual pistons of each nozzle may be staggered so that thepressure from the machine nozzle can remain constant.

[0062] In a further embodiment, the mold cavities 26 are of differentsizes. In order to fill each mold cavity 26 properly, the melt chamber54 of each nozzle 18 must be sized to accommodate the correct volume ofmelt. The nozzles 18 associated with each mold cavity 26 are identical;however, each injection piston 40 must be sized accordingly.

[0063] Although a preferred embodiment of the present invention has beendescribed, those of skill in the art will appreciate that variations andmodifications may be made without departing from the spirit and scopethereof as defined by the appended claims.

We claim:
 1. An injection molding apparatus comprising: a manifoldhaving a manifold channel for receiving a melt stream of moldablematerial under pressure, said manifold channel having an outlet fordelivering the melt stream to a nozzle channel of a nozzle; a moldcavity receiving said melt stream from said nozzle, said nozzle channelcommunicating with said mold cavity through a mold gate; a gatingmechanism for selectively closing said mold gate; an injection pistonextending through said nozzle channel of said nozzle and being slidabletherethrough, an outer wall of said injection piston abutting an innerwall of said nozzle channel, said injection piston being movable from aretracted position to an extended position to force melt towards saidmold cavity; a valve located at a forward end of said injection piston,said valve being selectively movable to block communication between arecess, which is provided in said outer wall of said injection pistonadjacent said valve, and a melt chamber of said nozzle channel, saidvalve being open to allow melt to flow from said manifold channel intosaid recess and into said melt chamber of said nozzle channel when saidinjection piston is in said retracted position; wherein movement of saidinjection piston towards said extended position forces melt located insaid melt chamber of said nozzle channel to flow into said mold cavity.2. An injection molding apparatus as claimed in claim 1, wherein apredetermined volume of melt is located in said melt chamber of saidnozzle channel.
 3. An injection molding apparatus as claimed in claim 2,wherein said gating mechanism is a valve pin driven by a piston.
 4. Aninjection molding apparatus as claimed in claim 2 wherein movement ofsaid injection piston from said retracted position to said extendedposition causes said valve to close.
 5. An injection molding apparatusas claimed in claim 2, wherein movement of said injection piston fromsaid extended position to said retracted position causes said valve toopen.
 6. An injection molding apparatus as claimed in claim 2, whereinmovement of said injection piston is controlled by a controller thatreceives information from a pressure sensor that senses the pressure ofat least one of said mold cavity, said nozzle channel and said manifoldchannel.
 7. An injection molding apparatus as claimed in claim 6,wherein said controller further receives information from a temperaturesensor that senses the temperature of at least one of said mold cavity,said nozzle channel and said manifold channel.
 8. A method of forcingmelt into a mold cavity of an injection molding apparatus, said methodcomprising: closing a mold gate of said mold cavity to block a meltstream from flowing from a nozzle channel of a nozzle into said moldcavity; maintaining an injection piston located in said nozzle channelin a retracted position, in which a valve located at a forward end ofsaid injection piston is open to enable the melt stream to flow from amanifold channel of a manifold, through a recess provided adjacent saidforward end of said injection piston into a melt chamber of said nozzlechannel, to fill said nozzle channel with melt; closing said valve toblock flow of the melt stream between said recess and said melt chamberof said nozzle channel; opening said mold gate; and moving saidinjection piston towards an extended position to force the melt locatedin said melt chamber of said nozzle channel into said mold cavity.
 9. Aninjection piston for a nozzle of an injection molding apparatuscomprises: a valve located on a forward end of said injection piston,said valve being selectively closable to block communication between arecess, which is provided in said outer wall of said injection pistonadjacent said valve, and a melt chamber of a nozzle channel; and whereinsaid valve is open to allow melt to flow from said recess past saidvalve when said injection piston is in a retracted position and saidvalve is closed when said injection piston is moved toward an extendedposition in order to force melt into a mold cavity.
 10. An injectionmolding apparatus comprising: a manifold having a manifold channel forreceiving a melt stream of moldable material under pressure, saidmanifold channel having an outlet for delivering the melt stream to anozzle channel of a nozzle; a mold cavity receiving the melt stream fromsaid nozzle channel, said nozzle channel communicating with said moldcavity through a mold gate; a gating mechanism for selectively closingsaid mold gate; a melt chamber located in said nozzle channel adjacentsaid mold gate, said melt chamber having a predetermined volume; a valvelocated between said outlet of said manifold channel and said meltchamber, said valve being selectively movable to control melt flow fromsaid manifold channel into said melt chamber; and wherein saidpredetermined volume of melt is injected into said mold cavity in asingle shot.
 11. The injection molding apparatus of claim 10, whereinsaid valve is located at a forward end of a injection piston, saidinjection piston being slidable within said nozzle channel to force meltfrom said melt chamber into said mold cavity.
 12. A method of injectinga predetermined volume of a molten material into a mold cavitycomprising: a) injecting molten material through a hot runner manifoldinto a valve gated hot runner nozzle including a movable valve pin,where the valve pin is in the closed position engaging a mold gate; b)opening the mold gate; c) injecting the molten material into a moldcavity through the mold gate by moving an injection piston located atleast partially in the nozzle to transfer the predetermined volume ofmolten material from the hot runner nozzle into the mold cavity. d)closing the communication between the hot runner nozzle and the moldcavity by moving the valve pin into engagement with the mold gate.
 13. Amethod as claimed in claim 12, wherein movement of said injection pistonis controlled by a controller that receives information from a pressuresensor that senses the pressure of at least one of said mold cavity,said nozzle channel and said manifold channel.
 14. A method as claimedin claim 13, said controller further receives information from atemperature sensor that senses the temperature of at least one of saidmold cavity, said nozzle channel and said manifold channel.
 15. A methodof injecting a predetermined volume of a molten material into a moldcavity comprising: a) injecting molten material through a hot runnermanifold into a valve gated hot runner nozzle including a movable valvepin, where the valve pin is in the closed position engaging a mold gate;b) blocking communication between the hot runner manifold and the hotrunner nozzle; c) opening the mold gate; d) moving an injection pistonlocated at least partially in the nozzle toward the mold gate totransfer the predetermined volume of molten material from the hot runnernozzle into the mold cavity; e) closing the communication between thenozzle and the mold cavity by moving the valve pin into engagement withthe mold gate.
 16. A method as claimed in claim 15, wherein movement ofsaid injection piston is controlled by a controller that receivesinformation from a pressure sensor that senses the pressure of at leastone of said mold cavity, said nozzle channel and said manifold channel.17. A method as claimed in claim 16, said controller further receivesinformation from a temperature sensor that senses the temperature of atleast one of said mold cavity, said nozzle channel and said manifoldchannel.